The “silicon revolution” drove the development of faster and larger computers beginning in the early 1960's giving rise to predictions of rapid growth because of the increasing numbers of transistors packed into integrated circuits with estimates they would double every two years. (“Moore's Law”) Since 1975, however, they doubled about every 18 months.
An active period of innovation in the 1970's followed in the areas of circuit design, chip architecture, design aids, processes, tools, testing, manufacturing architecture, and manufacturing discipline. The combination of these disciplines brought about the VLSI era and the ability to mass-produce chips with 100,000 transistors per chip at the end of the 1980's, succeeding the large scale Integration (“LSI”) era of the 1970's with only 1,000 transistors per chip. (Carre, H. et al. “Semiconductor Manufacturing Technology at IBM”, IBM J. RES. DEVELOP., VOL. 26, no. 5, September 1982). Mescia et al. also describe the industrial scale manufacture of these VLSI devices. (Mescia, N.C. et al. “Plant Automation in a Structured Distributed System Environment,” IBM J. RES. DEVELOP., VOL. 26, no. 4, (July 1982).
The release of IBM's Power6™ chip in 2007, noted “miniaturization has allowed chipmakers to make chips faster by cramming more transistors on a single slice of silicon, to the point where high-end processors have hundreds of millions of transistors. . . . ” (http://www.nytimes.com/reuters/technology/tech-ibm-power.html?pagewanted=print (2/7/2006))
More recently, “engineers did a rough calculation of what would happen had a 1971 Volkswagen Beetle improved at the same rate as microchips did under Moore's Law: ‘Here are the numbers: [Today] you would be able to go with that car 300,000 miles per hour. You would get two million miles per gallon of gas, and all that for the mere cost of 4 cents!’” T. Friedman, N.Y. Times, Op Ed, May 13, 2015.
Technology scaling of semiconductor devices to 90 nm and below has provided many benefits in the field of microelectronics, but has introduced new considerations as well. Smaller chip geometries result in higher levels of on-chip integration and performance, higher current and power densities, increased leakage currents, and low-k dielectrics all of which present new challenges to package designs.
Components fabricated with microelectromechanical systems (MEMS) are being incorporated in an increasing number of consumer applications including, but not limited to, automotive electronics, medical equipment, cell phones, hard disk drives, computer peripherals, and wireless devices. MEMS technology is directed at forming miniaturized electro-mechanical devices and structures using micro-fabrication techniques. MEMS devices are characterized by some form of mechanical functionality, which is typically in the form of a least one moving structure. Structures may be formed on a suitable substrate by a series of processing steps involving thin film depositions that are photolithographically masked and etched. MEMS mechanical elements, sensors, and actuators may be integrated on a common substrate with complementary metal-oxide-semiconductor (CMOS) devices.
Fabricators manufacture MEMS devices using processes and equipment developed for standard semiconductor integrated circuit chips, which allowed for microfabrication with increased precision, smaller devices, and generally devices having lower power requirements. One type of MEMS device that has wide applicability in the electronics industry comprises the MEMS switch which evolved from the increased need for miniature switches on semiconductor substrates along with other semiconductor components to form various types of circuits.
These miniature switches can act as relays and in many instances replaced field effect transistor switches (FETS) in microcircuits. Manufacturers employed MEMS switches to reduce insertion losses due to added resistance as well as parasitic capacitance and inductance inherent in FETS in a signal path. MEMS switches also find use in many radio frequency (RF) applications, such as antenna switches, load switches, transmit or receive switches, tuning switches, and the like. Some applications utilize multiple MEMS switches, with each having specific electrical requirements, mechanical requirements, or both. These applications require consistency of electrical characteristics or mechanical characteristics, or both.
MEMS switches rely on mechanical movement of a deflection electrode to make or break contact with a stationary electrode, thus forming a short circuit or an open circuit depending on the position of the deflection electrode. MEMS switches are typically actuated by using electrostatic forces to produce the mechanical movement required to change the state of the switch. MEMS switches are noted for their low power consumption, high isolation in the off state, low insertion loss in the on state, and high linearity, typically outperforming switches relying on semiconductor devices such as field-effect transistors (FETs). Switches provide an important building block in many electronic systems, and the performance characteristics of MEMS switches make them particularly attractive for providing signal switching functions in mixed signal, communications, and radio frequency integrated circuit applications.
One of the devices comprise MEMS-based relays for application in radio frequency (“RF”) communication technologies because the switching characteristics of a MEMS relay is superior to those of traditional switches like the GaAs MESFET, and the p-i-n diode. For example, MEMS relays have lower power consumption rates, lower insertion losses, and higher linearity. All these features make MEMS relays a great candidate for wireless communication applications like wireless transceivers in cellular phones.
MEMS switches require large voltages to actuate the switch. Fabricators term this as a “pull-down,” or “pull-in,” or actuation voltage, which is anywhere from 20 to 40 volts or more. A typical MEMS switch uses electrostatic force to cause mechanical movement that result in electrically bridging a gap between two contacts such as in the bending of a cantilever. In general this gap is relatively large in order to achieve large impedance during the “off” state of the MEMS switch. Consequently, this large pull-down voltage electrically bridges the large gap, while a smaller maintaining voltage maintains the bridge. These high pull-down voltages can cause arcing and consequent oxidation in the switch which contributes to its eventual breakdown. Even so, a typical MEMS switch has a useful life of approximately 108 to 109 cycles, but fabricators nonetheless have an interest in increasing the lifetime of these switches.
MEMS microswitches, including those with very low contact forces, are also very sensitive to any organic or other contamination occurring on the contact surfaces. Therefore, these switches are typically packaged or sealed as early as possible in the manufacturing process in an inert ambient environment. This environment is typically a mixture of inert gases such as N2, Ar and the like, where the pressure vary between atmospheric pressure and higher. For larger switches, such as relays, getters are commonly used within the package to accumulate any contamination which may arise in the package. This method works very well for larger packages, but for micro-scale switches such as MEMS switches, including a getter within the package may be very challenging if not impossible for small cavities created in fabricating the switches. Therefore, a clean environment consisting of an inert gas such is typically employed in the small cavity.